This invention relates to generally to polymer-metal-precursor composites and particularly to a polymer-metal-precursor composite in which the metal-precursor component is a tungsten precursor.
X-ray and gamma ray sources are presently being used in a wide array of medical and industrial machinery, and the breadth of such use expands from year to year. Consumer tend to notice medical and dental X-ray machines, but in addition to these applications there are baggage screening machines, CAT scan machiness, non-destructive industrial inspection machinery and ion implantation machines used in the manufacture of silicon wafer computer chips. All require that radiation be contained and directed.
In the past, lead itself or lead-polymer composites were used to make such items. But there are numerous problems with the use of lead. One problem with lead is that it is toxic and thus subject to increasingly stringent legal controls. Another issue is that lead may not have the mechanical or electrical properties desired for a given application. Lead has been used in various forms in wide range of applications: machined, as a solid casting, as a solid encased within a matrix such as a polymer matrix, or as a filler. As a filler, it may be lead particles, tribasic lead-sulfate or lead-oxide particles or particles of a specified shape or size, or as a mixture with other materials such as tin. Tungsten shielding, or polymer-tungsten shielding has also been used. Examples of all of these methods may be found in the prior art.
Polymer-metal composite materials are of increasing importance in radiation technology and a number of industries, due to the fact that polymer-metal composite materials offer characteristics which are difficult or impossible to match in other materials of equivalent price or ease of manufacture.
In general, polymer-metal composites are materials having a polymer matrix containing particles of a metal compound intermixed therein. The polymer may advantageously have plastic properties allowing for ease of manufacture, but a wide variety of polymers are known for use in such composites. The choice of metal will place undesirable limitations on the range of properties which may be provided to the manufactured composite. In general, high density and accompanying factors such as increased mass, increased radiological shielding properties, heat-deflection properties, impact strength, tensile strength and so on. In the prior art, lead has been a particularly favored material for its density and ease of working. Tungsten has been favored more recently. Three characteristics in particular which make such materials desirable are electrical non-conductivity, radiological shielding ability, and high density.
There is a growing list of applications for which polymer-metal composite materials are either required or advantageous. Reactor shielding, ion implantation machine source insulators, X-ray tube housings, radioisotope housings, syringe housings, body shielding, dental X-ray packets (xe2x80x9cbitewingsxe2x80x9d), containers, other castings and housings all benefit from the properties of polymer-metal composite materials. In the case of typical high voltage insulators for ion implantation machinery, a thick walled generally round or cylindrical part is created out of lead or polymer-lead-oxide ranging from an inch to several feet or more in long dimension and weighing anywhere up to 500 pounds. Wall thickness may range from xc2xd inch to several inches. Such parts must resist high voltages, shield against x-ray or gamma ray emission and hold a high vacuum state when connected to the vacuum chamber. X-ray tube shielding is generally thinner (often 0.070 inch thickness), generally smaller, and of different shape, having an aperture for the X-ray beam, but once again must offer high voltage insulation and radiation protection. The lead in such devices obviously presents an environmental challenge to manufacture, use and disposal.
In the processing of lead precursor filled plastics known in the art, specialized facilities, handling procedures, training and safety equipment must be used to protect the employees from the lead precursor they handle. Lead-based dust is a particular concern, being airborne and inhalable. Such dust may be generated during mixing, molding, deflashing, machining and finishing of final products such as insulators or shields, to say nothing of earlier stages of mining, smelting and refining of lead and the final disposal of the used product at the end of its useful life. Even during the life span of the product, it is illegal to sand, machine, alter or use the product in any way that will generate dust. All such processes must be carried out at special lead handling sites, and all waste dust from any of these processes must be collected in accordance with OSHA regulations and transported to hazardous waste land fills in accordance with OSHA and DES guidelines.
Internalized by law into the manufacturing process, such safety issues dramatically increase the cost of such products, which in turn increases other medical or industrial costs.
One attempt to deal with the issue of environmental lead contamination may be found in U.S. Pat. No. 6,048,379 issued Apr. 11, 2000 to Bray et al for xe2x80x9cHIGH DENSITY COMPOSITE MATERIALxe2x80x9d. This patent teaches the use of tungsten powder, a binder and a polymer to provide a composite material offering a density high enough for use as ammunition. As stated in that patent""s xe2x80x9cDescription of Related Artxe2x80x9d, xe2x80x9cThe density of the projectile should be close to that of a lead projectile for realistic performance simulation. Materials of a lower density decrease projectile range and penetration.xe2x80x9d Thus this patent teaches towards higher density materials. In addition, tungsten is electrically conductive and thus tungsten composite mixes do not provide any significant electrical insulation. Another serious issue with the use of tungsten is that of cost. Tungsten metal is quite expensive in comparison to lead. For example, tungsten-composite materials may cost as much as 20$ per pound.
U.S. Pat. No. 5,730,664, U.S. Pat. No. 5,719,352, and U.S. Pat. No. 5,665,808, respectively issued to Asakura, Griffin, Bilsbury all disclose metal-polymer composites for projectiles, respectively golf balls and shot pellets. Other patents from the same art (projectiles) also propose non-toxic materials.
In the radiation shielding art itself, various patents propose polymer-metal composites of various forms.
EcoMASS (a registered trademark of the PolyOne Corporation) is a combination of tungsten metal and nylon and elastomer compounds used for shielding, apparently based upon the Bray ""379 patent related to ammunition and thus developed specifically in response to military/sporting needs for non-toxic ammunition. It does not teach that materials other than tungsten may be used, thus limiting the range of characteristics of the final product. For example, tungsten is electrically conductive and thus is not normally suitable for insulators. As mentioned earlier, this material also faces cost limitations. In addition, this material has manufacturing limitations in terms of thickness and size of the final item.
U.S. Pat. No. 4,619,963 issued Oct. 28, 1986 to Shoji et al for xe2x80x9cRADIATION SHIELDING COMPOSITE SHEET MATERIALxe2x80x9d teaches a lead-tin fiber and resin shield, as does U.S. Pat. No. 4,485,838 issued Dec. 4, 1984 to the same inventors.
U.S. Pat. No. 6,310,355 issued Oct. 30, 2001 to Cadwalader for xe2x80x9cLIGHTWEIGHT RADIATION SHIELD SYSTEMxe2x80x9d teaches a flexible matrix having a radiation attenuating material and at least one void.
U.S. Pat. No. 6,166,390 issued Dec. 26, 2000 to Quapp et al for xe2x80x9cRADIATION SHIELDING COMPOSITIONxe2x80x9d teaches a concrete composite material.
U.S. Pat. No. 5,360,666 issued Nov. 1, 1994 and U.S. Pat. No. 5,190,990 issued Mar. 2, 1993 to Eichmiller for xe2x80x9cDEVICE AND METHOD FOR SHIELDING HEALTHY TISSUE DURING RADIATION THERAPYxe2x80x9d teach a radiation shield for the human body comprising an elastomeric material and certain mixtures (see the summary of the invention) of various metals in the form of spherical particles.
General Summary
The present invention teaches a novel family of lead-free plastic materials that may act as replacements for lead or lead oxide filled plastics, particularly in the role of radiation shields and insulators. The present invention teaches a polymer-tungsten-precursor composite comprising a plastic matrix having high density tungsten precursor materials within it as xe2x80x9cfillerxe2x80x9d. By tungsten precursors are meant raw materials used in the manufacture of tungsten including but not limited to tungsten oxide, ammonium paratungstate (APT), ammonium metatungstate (AMT), etc. Tungsten precursors have a reduced electrical conductivity and thus tungsten-precursor composites allow the manufacture of insulators. Such tungsten-precursors may range in price from ⅓ to ⅔ the cost of tungsten metal, thus decreasing price of the final product, yet may contain over 80% of the tungsten of tungsten metal, thus offering a commercial benefit: tungsten-precursors may be advantageously manufactured for 8$ per pound.
The present invention further teaches that by use of a number of such tungsten-precursors the range and breadth of the material characteristics which may be achieved is expanded. This flexibility allows a wider range of function and use when compared with previous methods using a single metal or a single metal and polymer composite.
The present invention further teaches the use of binders, fibers, and secondary fillers in the polymer-tungsten-precursor composite in order to further broaden the range of achievable desirable physical, radiological and/or electrical properties.
Summary in Reference to Claims
The present invention in the presently preferred embodiment and best mode presently contemplated for carrying out the invention teaches a radiation shield material comprising: a polymer matrix and a tungsten-precursor within the polymer matrix.
In further embodiments, the invention teaches a radiation shield material wherein the tungsten precursor comprises at least one member selected from the following group: ammonium paratungstate, ammonium metatungstate, blue tungsten oxide, yellow tungsten oxide and combinations thereof.
In further aspects, the present invention teaches a radiation shield material wherein the tungsten precursor comprises tungsten oxide in an amount ranging from approximately 80% to approximately 99.9% of the total weight of the tungsten precursor.
It is one objective of the present invention to teach a radiation shield material wherein the tungsten precursor comprises an amount by volume approximately ranging from 5% to 95%, preferably 10% to 50% of the total composite volume.
The present invention further teaches a radiation shield material wherein the polymer matrix comprises at least one member selected from the following group: thermosetting material, thermoplastic material and combinations thereof.
The present invention further teaches a radiation shield material wherein the polymer matrix comprises at least one member selected from the following group: epoxy, polyester, polyurethane, silicone rubber, bismaleimides, polyimides, vinylesters, urethane hybrids, polyurea elastomer, phenolics, cyanates, cellulose, flouro-polymer, ethylene inter-polymer alloy elastomer, ethylene vinyl acetate, nylon, polyetherimide, polyester elastomer, polyester sulfone, polyphenyl amide, polypropylene, polyvinylidene florid, acrylic, homopolymers, acetates, copolymers, acrylonitrile-butadiene-styrene, flouropolymers, ionimers, polyamides, polyamide-imides, polyacrylates, polyether ketones, polyaryl-sulfones, polybenzimidazoles, polycarbonates, polybutylene, terephthalates, polyether sulfones, thermoplastic polyimides, thermoplastic polyurethanes, polyphenylene sulfides, polyethylene, polypropylene, polysulfones, polyvinylchlorides, styrene acrylonitriles, polystyrenes, polyphenylene, ether blends, styrene maleic anhydrides, allyls, aminos, polyphenylene oxide, and combinations thereof.
The present invention has a further advantage in teaching a radiation shield material wherein the polymer matrix comprises epoxy resin in an approximate amount of 55% by volume and further wherein the tungsten precursor comprises blue tungsten oxide powder in an approximate amount of 45% by volume.
The present invention further has as one aspect the teaching of a radiation shield material further comprising a third material.
The present invention further teaches alternative embodiments of a radiation shield material wherein the third material comprises at least one member selected from the following group: electrically insulating materials, binders, high density materials and combinations thereof.
In embodiments, the present invention teaches a radiation shield material wherein the third material comprises at least one member selected from the following group: tungsten metal, calcium carbonate, hydrated alumina, tabular alumina, silica, glass beads, glass fibers, magnesium oxide, wollastonite, stainless steel fibers, copper, carbonyl iron, iron, molybdenum, nickel and combinations thereof.
The present invention yet further teaches a radiation shield material wherein the third material comprises an amount by volume approximately ranging from 5% to 95%, preferably 10% to 30% of the total composite volume.
The present invention further teaches a radiation shield material wherein the polymer matrix comprises epoxy resin in an approximate amount of 64% of the total composite volume, and further wherein the tungsten precursor comprises blue tungsten oxide powder in an approximate amount of 16% by volume, and further wherein the third component comprises hydrated alumina in an approximate amount of 20% by volume.
In another embodiment, the present invention teaches a radiation shield comprising the material of claim 1.
In another embodiment, the present invention teaches that the radiation shield is used as an ion source insulator.
It is a further embodiment, advantage, aspect and objective of the present invention to teach a radiation shield comprising a body comprising a polymer matrix and a tungsten precursor within the polymer matrix.
The present invention further teaches a radiation shield wherein the body has a shape selected from the following group: generally annular bodies, generally cylindrical bodies, three dimensional conic sections, regular prisms, irregular prisms and combinations thereof.
The present invention further teaches that the radiation shield may be utilized as an ion source insulator.
The present invention further teaches a method of making a radiation shield comprising combining a tungsten precursor and a polymer into a composite; and forming the composite into a desired shape.
The present invention further teaches a method wherein the step of forming the composite into the desired shape further comprises one member selected from the following group: casting, molding, machining, extrusion, aggregation, liquid resin casting, injection molding, compression molding, transfer molding, pultrusion, centrifugal molding, calerendering, filament winding and combinations thereof.